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Children with Down Syndrome

Children with Down syndrome have a tenfold to twentyfold increased risk of leukemia compared with children without Down syndrome; the ratio of acute lymphoblastic leukemia to acute myeloid leukemia (AML) is nevertheless typical for childhood acute leukemia. The exception is during the first 3 years of life, when AML, particularly the megakaryoblastic subtype, predominates and exhibits a distinctive biology characterized by GATA1 mutations and increased sensitivity to cytarabine.[1-9] Importantly, these risks appear to be similar whether a child has phenotypic characteristics of Down syndrome or whether a child has only genetic bone marrow mosaicism.[10]

In addition to increased risk of AML during the first 3 years of life, about 10% of neonates with Down syndrome also develop a transient myeloproliferative disorder (TMD) (also termed transient leukemia). This disorder mimics congenital AML, but typically improves spontaneously within the first 3 months of life, though TMD can remit as late as 20 months.[11] Although TMD is usually a self-resolving condition, it can be associated with significant morbidity and may be fatal in 10% to 20% of affected infants.[11-13] Infants with progressive organomegaly, visceral effusions, preterm delivery (less than 37-weeks gestation), bleeding diatheses, failure of spontaneous remission, laboratory evidence of progressive liver dysfunction (elevated direct bilirubin), and very high white blood cell count are at particularly high risk for early mortality.[12,14] Death has been reported to occur in 21% of these patients with high-risk TMD.[15] Three risk groups have been identified based on the diagnostic clinical findings of hepatomegaly with or without life-threatening symptoms: (1) low risk includes those with neither finding (38% of patients and 92% ± 8% OS); (2) intermediate risk with hepatomegaly alone (40% of patients and 77% ± 12% overall survival [OS]); and (3) high risk with both characteristics (21% of patients and 51% ± 19% OS).[15] Therapeutic intervention is warranted in patients in whom severe hydrops or organ failure is apparent. Several treatment approaches have been used, including exchange transfusion, leukapheresis, and low-dose cytarabine.[16]

The mean time for the development of AML in the 10% to 30% of children who have a spontaneous remission of TMD but then develop AML has been reported to be approximately 16 months, with a range of 1 to 30 months.[11,15,17] Thus, most infants with Down syndrome and TMD who later develop AML will do so within the first 3 years of life. Patients with Down syndrome who develop AML with an antecedent TMD have superior event-free survival (EFS) (91% ± 5%) compared with such children without TMD (70% ± 4%) at 5 years,[14] although this was not observed in another study.[18] While TMD is generally not characterized by cytogenetic abnormalities other than trisomy 21, the presence of additional cytogenetic findings may connote an increased risk for developing subsequent AML.[12]

Outcome is generally favorable for children with Down syndrome who develop AML.[18,19] The prognosis is particularly good (EFS exceeding 80%) in children aged 4 years or younger at diagnosis, the age group that accounts for the vast majority of Down syndrome patients with AML.[18,20] A large study of 451 children with AML and Down syndrome (age >6 months and <5 years) confirmed the generally favorable outcome for this patient population (7-year EFS of 78% and 7-year OS of 79%).[21] Multivariate analyses revealed that white blood cell (WBC) count (≥20 × 109/L) and age (>3 years) were independent predictors for lower EFS, although 7-year EFS for the older population (>3 years) and for the higher WBC count population still exceeded 60%. Absence of leukemia cell cytogenetic abnormalities (other than trisomy 21), observed in approximately 30% of patients, independently predicted for inferior OS and EFS (7-year EFS of 65% compared with 82% for patients with aberrant karyotypes).

Appropriate therapy for younger children (aged ≤4 years) with Down syndrome and AML is less intensive than current standard childhood AML therapy, and hematopoietic stem cell transplant is not indicated in first remission.[3,17,18,20,22-25]

Children with mosaicism for trisomy 21 are recommended to be treated similarly to those children with clinically evident Down syndrome.[10] Children with Down syndrome who are older than 4 years have a significantly worse prognosis.[23] Although an optimal treatment for these children has not been defined, they are usually treated on AML regimens designed for children without Down syndrome.